The present invention relates to a process of obtaining solid elastomeric products, containing a filler, in the form of dry free flowing powders which do not conglomerate or experience flaking or separation of the resin coating or filler during storage and handling and which can be used for injection molding of elastomeric articles. To incorporate a filler into an elastomer normally requires the use of rolling mills or internal mixers. The operation of these machines require large expenditures of energy. In these times of energy shortages it was desirous to find a method of avoiding large energy expenditures. It was for this reason an investigation was made for a method of incorportion of a filler into an elastomer to form a pourable powder without resorting to these high energy using machines. It was also of interest to convert the rubber to a form in which automated equipment could be used in handling the product during processing.
A large number of references are cited which deal with pulverulent elastomeric mixtures and with the possibilities of pulverized elastomer technology. Only recently have methods been disclosed for making pulverulent pourable elastomer mixtures such as elastomer-carbon black mixtures.
U.S. Pat. Nos. 3,920,604 and 3,945,978 describe a process of preparing an elastomer containing a filler by emulsifying a solvent solution of the elastomer and the filler, flashing off the solvent and coagulating the mixture to a pourable powder.
Also of interest is U.S. Pat. No. 4,073,755, which describes a process for the production of pulverulent, tack-free, pourable filler-containing elastomer particles by precipitating a stable emulsified homogeneous mixture of an aqueous elastomer emulsion and an aqueous dispersion of a solid filler in the presense of sodium silicate, separating the thus precipitated elastomeric mixture from water and drying the mixture to a tack-free powder. Although this method initially gives a tack-free powder, the powder tends to conglomerate on storage when exposed to the atmosphere. This is probably caused by the silicic acid used to coagulate the mixture. After coagulation the resultant acid solution is neutralized to form a salt which is partly incorporated in the elastomer-filler powder and is not readily removed, even by washing. When exposed to the atmosphere the resultant salt deliquesces causing the particles to conglomerate.
A method of making a resin encapsulated elastomer is described in U.S. Pat. No. 3,813,259. In that invention the rubber is coated with a resin partitioning agent by agglomerating the resin from its latex at a specific temperature which must be within 5.degree. C. of the agglomeration temperature of the resin. This temperature is critical for the adherence of the resin coating to the elastomer.
According to the present invention the preceding problems with the products and processes are eliminated. The pulverulent elastomer when exposed to the atmosphere on storage remains dry and does not conglomerate. The elastomer slurry can be coated with this resin in a wider temperature range and at one much lower than the agglomeration temperature without flaking or separation of the resin from the elastomer. The invention also incorporates the carbon black into the elastomer without the use of high energy equipment.